Automatic screw machines, and other multiple spindle machine tools, are well-known in the art. These machines have the capacity for producing high volumes of items, such as screws, bolts and pipe fittings efficiently and effectively.
Generally, multi-spindle screw machines consist of four to eight rotatable spindles equally spaced about a rotatable drum, or spindle carrier. Each spindle is equipped with a chuck for holding a workpiece in place during maching. Bar stock is fed through one end of the spindle to be formed into the workpiece. The spindle carrier rotatably indexes about a central axis positioning each spindle at a selected workstation. Each workstation consists of working tools attached to indexing cross and end slides. The slides are advanced until the working tools come into contact with the stock and are retracted after the work has been completed. After the tools from each station are retracted, the drum rotates the appropriate distance, depending upon the number of spindles, thus locating each spindle in the appropriate position for a sequential operation. A final tool slide is usually provided with a cutting tool which cuts the workpiece from the bar stock, completing the process that is then repeated.
In the past, automatic screw machines were equipped with a single power source normally referred to as a drive motor. The drive motor provided power to rotate each spindle, as well as the power for reciprocating the cross and end slides into the working and retracted positions. The drive motor provided power to the rest of the machine by driving a main shaft. A spindle shaft rotated each spindle at the appropriate speed and was driven by the main shaft through a set of high and low speed gears. These gears rotated a secondary shaft at either high or low speeds that in turn, rotated the spindle drive shaft at a high or low speed. A geartrain was used to transfer power from the secondary shaft to the spindle shaft.
The main shaft also provided power to the tool slides through a set of clutches, worm gears, shafts and geartrains. The clutch system was engaged or disengaged by a shaft rotated by a small worm gear, driven by a shaft connected by way of a geartrain to the spindle drive shaft. The clutch would engage or disengage depending upon whether the spindle shaft was rotating at a high or low speed, respectively. During low speed operation the tool contacted the workpiece and the slide indexed slowly along the length of the piece to ensure precision and reduce heat and tool wear. The high speed clutch indexed the tools into a machining position from their retracted position and back to the retracted position after the machining operation was completed. Retracting the tool slides allowed the spindle carrier to rotate and position each workpiece in the next workstation. This rapid indexing of the tool slides facilitates significant reduction in cycle time, thus allowing increased productivity.
Problems inherent in conventional automatic screw machines are due to their inflexibility. They cannot readily handle tasks which they are not precisely designed to perform. Such tasks may substantially change over time. Cost and time associated with maintenance and repair of the significant number of wearing parts also cannot readly.
Changing over a machine in the past to handle machining jobs other than what the machine was originally designed to accomplish tended to require extensive changes to the machine including changes to the high/low drive gears and clutch system, and could involve the drum shaft and several gear trains.
Other attempts have been made to integrate the existing designs with electronic control systems in an attempt to blend the utility of these machines with modern manufacturing processes. It has not been feasible to retrofit existing machines with comprehensive electronic controls due to the costs associated with such a retrofit.